Never. Babies cry for a reason, and yes comfort aka being held, is a real reason. Some babies want to be held more than others, and I still comfort my 6 and 3 year olds, it's normal. Adults even need touch and comfort (many adults cuddle, etc). You won't make your babies spoiled as toddlers/older kids, or anything of the sort. All that hoopla is a myth (and yes, it's been studied). I always held my babies, never let them cry, and I have very independent kids. In fact, not more than 10 minutes ago they came up to me while doing dishes, said goodnight and went to bed (I didnt' even tell them to go to bed).